Abstract
Keywords: engine, cold cranking, starter, battery, simulation
Engine starting is a very complex phase which involves electrical devices (battery-harnessstarter) as well as mechanical and thermal events. Because of the coupling of various physics domains during transient operation, predetermination of the global system performances is very hard, and the choice of battery and starter in accordance with technical and operational requirements can thus be quite hard to optimize. This difficulty is amplified by the dispersion of parameters which have to be taken into account. Not only the parameters of the various components have to be considered, but also the ambient temperature or the oil quality, as oil viscosity has a high influence on the mechanical torque.
Validation of the electrical starting system (battery-harness-starter) is mainly based on tests in climatic rooms, using engine benches or vehicles. But such tests are always long and hard to carry out. To reach realistic temperature conditions, it is necessary to let the car in the climatic room for a long time, up to 24 hours for very low temperature, so that the battery temperature can decrease until a stabilized value. Moreover, taking into account the dispersion of various parameters is very hard through actual tests. In the development cycle of a vehicle, actual tests can be performed only quite late, and the risk for late modifications can´t be excluded. This is particularly dangerous for devices like the battery which has a great impact on the underhood architecture.
The development of a simulation tool to reproduce cold cranking appears as a possible way to limit the number of actual tests and also to justify robust choices in the starting system design as early as possible in the development cycle.